1. Field of the Invention
The present invention relates to an electrode for dielectric barrier discharge treatment of a substrate, the electrode comprising a tubular housing that is made of electrically insulating material and having a bottom wall facing the substrate, two side walls extending away from the substrate, and a top wall connecting the distal ends of the side walls. The electrode further comprises an electrically conductive electrode member disposed inside the housing and having a plate that engages an internal surface of the bottom wall of the housing and two wings formed in one piece with the plate and engaging internal surfaces of the side walls of the housing.
2. Background of the Invention
A dielectric barrier discharge treatment such as a plasma treatment or corona treatment is frequently employed for modifying the surface tension of a substrate in order to improve, for example, the adhesion of a coating layer, an ink layer or the like that is to be applied to the surface of the substrate.
EP 0 621 667 A2 shows an electrode of the type mentioned above, wherein the electrode member is tubular and water cooled, and the housing is formed by a ceramic coating on the electrode member.
EP 1 919 048 A1 discloses a corona electrode, wherein the housing is made of ceramic material and the electrode is configured as a flat plate that engages the bottom wall of the housing and extends between the opposite side walls of the housing.
When an electrode having this design is to be employed for plasma treatment, a high voltage with high frequency is applied to the electrode member, thereby creating an oscillating electric field that excites a gaseous medium (ambient air or a suitable treatment gas) that is present in the space between the electrode and the surface of the substrate to be treated, so that the gaseous medium is turned into a plasma. In the process of generating the plasma, a considerable amount of heat is generated inside the electrode plate. It is thereby necessary to cool the electrode in order to prevent the ceramic housing from being over-heated.
In order to control the temperature of the electrode, it is possible to circulate a cooling medium, e.g. air, through the tubular housing.